1. Field of the Invention
This invention relates to a mechanism for shifting a pancratic lens assembly to provide varying magnifications, and more particularly to a mechanism for both positioning a lens assembly and moving the optical elements of the assembly relative to one another to provide a registered and focused image of an illuminated object at varying magnifications when the overall image-to-object distance is constant for all magnifications.
2. Description of the Prior Art
In the art of photocopying, light images of an illuminated object are exposed on a photosensitive target. Depending upon the size of the original object and the ultimate use of the recorded photocopy, a particular photocopier may be required to function over a plurality of magnification ratios. If the object plane and image plane are at a fixed separation distance, in order to provide variable magnifications, the lens assembly of the photocopier must be moved along the optical axis toward or away from the image plane. The light image is maintained in focus at the image plane for the varying positions of the lens assembly by the use of add lenses or multiple focus lens assemblies.
It has for some time been realized that variable magnification capabilities would be desireable in the field of electrophotocopying. Some examples of variable magnification copying apparatus used in electrophotography are U.S. Pat. Nos. 3,765,760; 3,778,147; 3,829,209; and 3,873,189. As may be readily seen from these patents, many different arrangements have been tried to provide efficient structure for a variable magnification electrophotographic copier apparatus. Additionally, U.S. Pat. No. 3,829,209 points out another problem which particularly concerns variable magnification electrophotographic copiers with fixed image-to-object distance; i.e., some compensation mechanism is required to maintain registration of an object point in the image plane at varying magnifications, such as movement of the lens assembly oblique to the optical axis.